1. Field of the Invention
The invention relates to a switchover valve and to an internal combustion engine.
2. Description of the Related Art
The compression ratio of an internal combustion engine defines the ratio between the entire cylinder chamber before compression and the remaining cylinder chamber after compression. A high compression ratio has a positive effect on engine efficiency. Some internal combustion engines, such as Otto-cycle engines, have applied ignition and a fixed compression ratio. Thus, the compression ratio for these engines must be selected to be only so high to prevent so-called “knocking” of the internal combustion engine in full-load operation. However, for the much more commonly occurring part-load range of the internal combustion engine, that is to say in the presence of a low cylinder charge, the compression ratio can have higher values without “knocking” occurring. The important part-load range of an internal combustion engine can be improved if the compression ratio is variably adjustable.
DE 10 2010 016 037 A1 discloses an internal combustion engine with an adjustable compression ratio. The engine has connecting rod with a crankpin bearing eye and a connecting-rod bearing eye. The connecting rod is connectable to a crankshaft by way of the crankpin bearing eye and to a cylinder piston of the internal combustion engine by way of the connecting-rod bearing eye. The connecting rod is assigned an eccentric adjustment device that has an eccentric body and eccentric rods.
The eccentric body of DE 10 2010 016 037 A1 has a piston-pin bore arranged eccentrically with respect to a central point of the connecting-rod bearing eye. The piston-pin bore has a central point and receives a piston pin. The eccentric adjustment device functions to adjust an effective connecting-rod length Ieff. The connecting rod length is the distance between the central point of the piston-pin bore and a central point of the crankpin bearing eye. The eccentric rods of the eccentric adjustment device are displaceable for rotating the eccentric body and thus varying the effective connecting rod length Ieff. Each eccentric rod has a piston that is guided displaceably in a hydraulic chamber. A hydraulic pressure prevails in the hydraulic chambers and acts on the pistons assigned to the eccentric rods. Displacement of the eccentric rods is possible or not possible in a manner dependent on the amount of oil in the hydraulic chambers.
The adjustment of the eccentric adjustment device is initiated by the action of inertial and load forces of the internal combustion engine that act on the eccentric adjustment device during a working stroke of the internal combustion engine. The directions of action of the forces acting on the eccentric adjustment device vary constantly during a working stroke. The adjustment movement is assisted by the pistons that are acted on by hydraulic oil and that act on the eccentric rods. The pistons prevent a restoring movement of the eccentric adjustment device due to varying directions of action of the forces acting on the eccentric adjustment device. The eccentric rods that interact with the pistons are connected to the eccentric bodies on both sides.
The hydraulic chambers in which the pistons are guided can be charged or filled with hydraulic oil from the crankpin bearing eye via hydraulic oil feed lines. Check valves prevent the hydraulic oil from flowing back from the hydraulic chambers into the hydraulic oil feed lines. A switchover valve is accommodated in a bore of the connecting rod. The hydraulic chambers are in contact via hydraulic oil discharge lines with the bore that accommodates the switchover valve. The switching position of the switchover valve determines which of the hydraulic chambers is filled with hydraulic oil and which of the hydraulic chambers is evacuated, and the adjustment device or direction of rotation of the eccentric adjustment device is dependent on this.
The switchover valve of DE 10 2010 016 037 A1 comprises an actuation element, a restoring spring and a control piston.
As noted above, the hydraulic oil that acts on the pistons that are guided in the hydraulic chambers of the eccentric rods is supplied to the hydraulic chambers from the crankpin bearing eye via the hydraulic oil feed lines. The connecting rod engages on the crankshaft by way of the crankpin bearing eye, and a connecting-rod bearing shell is arranged between a crankshaft journal of the crankshaft and the crankpin bearing eye.
The hydraulic chambers can be vented via the hydraulic oil discharge lines, in a manner dependent on the switching position of the switchover valve. The adjustment direction or direction of rotation of the eccentric adjustment device is dependent on this.
DE 10 2005 055 199 describes an internal combustion engine with an adjustable compression ratio and a connecting rod length that is variably adjustable. The variation of the connecting rod length is realized by way rotation of an eccentric connecting-rod eye. Rotation of the connecting-rod eye is initiated by the action of inertial and gas forces of the internal combustion engine. The rotational movement is assisted by pistons that are acted on with engine oil in the connecting rod. Rotational movement of the eccentric connecting-rod eye is regulated by acting on one of the pistons with engine oil pressure while relieving the other piston of pressure. The pistons are controlled by a 3/2 directional valve that must be actuated mechanically for the switchover. This control involves a cumbersome solution with slotted-guide tracks, switching rods and push rods that are actuated externally, for example, by electric motor means. Thus, comprehensive modifications to the internal combustion engine are required.
The prior art switchover valve enables the direction of adjustment or direction of rotation of the eccentric adjustment device to be influenced in an effective manner. However, there is a demand for a switchover valve that can be manufactured and assembled in a simple manner and that requires little structural space for actuation.
It is an object of the invention to provide a novel switchover valve for an internal combustion engine with an adjustable compression ratio, and an internal combustion engine having a switchover valve of said type.